1. Field of the Invention
This invention relates to an improvement in a fluid hydrocoking process. More particularly, this invention relates to a fluid hydrocoking process in which certain metal compounds are added to the chargestock.
2. Description of the Prior Art
Fluid coking is a well known process which may be carried out with or without recycle of the heavier portion of the fluid coking zone effluent. As is well known in the art, the fluid coking process, as shown, for example, in U.S. Pat. No. 2,881,130, which is hereby incorporated by reference, uses a fluid coking vessel and an external heating vessel. A fluid bed of solids, preferably coke particles produced by the process having a size in the range from about 40 to about 1000 microns is maintained in the coking zone by the upward passage of a fluidizing gas, usually steam, injected at a superficial velocity usually between 0.5 and 5 feet per second. The temperature of the fluid coking bed is maintained in the range of from about 850.degree. to about 1400.degree. F., preferably between 950.degree. and 1100.degree. F. by circulating solids (coke) to the heating vessel and back. The heavy oil to be converted is injected into the fluid bed and upon contact with the hot solids undergoes pyrolysis evolving lighter hydrocarbon products in vapor phase, including normally liquid hydrocarbons, and depositing a carbonaceous residue (coke) on the solids. The turbulence of the fluid bed normally results in substantially isothermal reaction conditions and thorough and rapid distribution of the heavy injected oil. Product vapors, after removal of entrained solids, are withdrawn overhead from the coking zone and sent to a scrubber and fractionator for cooling and separation. The end boiling point of distillate fraction obtained from the process is usually 1050.degree. to about 1200.degree. F. and the remaining heavy ends are usually recycled to extinction.
It is known to add hydrogen to a fluid coking zone (hydrocoking); see, for example, U.S. Pat. Nos. 2,888,395 and 2,888,393. High pressure by hydrocoking is known; see, for example, U.S. Pat. No. 2,885,350. The addition of hydrogen sulfide to the treat gas of a fluid coker including the addition of hydrogen sulfide to a hydrogen-containing treat gas is known; see, for example, U.S. Pat. No. 4,051,016. It is also known to use oil soluble organometallic compounds in thermal cracking or in destructive hydrogenation of hydrocarbons; see, for example, U.S. Pat. No. 1,876,270.
It is also known to conduct cracking or destructive hydrogenation in the presence of oil soluble salts of acid organic compounds selected from the group consisting of carboxylic acids and phenol with a metal of Group IV and Group VIII of the Periodic Table; see, for example, U.S. Pat. No. 2,091,831.
A slurry hydrocracking process is also known in which an oil soluble compound of Groups IV to VIII is added to a heavy oil feed; see, for example, U.S. Pat. No. 3,131,142.
It has now been found that the addition of a minor amount of certain metal compounds which act as coke forming inhibitors to the chargestock of a fluid hydrocoking process operated at elevated pressures will provide advantages that will become apparent in the ensuing description.